1. Field of the Invention
The present invention relates to integrated circuit packaging technology.
2. Background Art
A printed circuit board (PCB), also referred to as printed wiring board (PWB), is used to mechanically support and electrically connect electronic components mounted to the PCB. A PCB includes a stack of conductive and non-conductive layers attached together (e.g., laminated together). Conductive pathways (e.g., traces) are formed in the conductive layers (e.g., by etching) that are used to electrically connect the mounted electronic components.
Examples of electronic components that may be mounted to PCBs are integrated circuit (IC) packages. IC packages typically include one or more chips/dies (e.g., from semiconductor wafers), and are used to environmentally protect the dies and to interface the dies to PCBs. IC packages may be configured in various ways to be mounted to a PCB, including having arrangements of pins, pads, solder balls, etc., that are used to mechanically secure the IC package to the PCB, as well as to electrically connect signals of the IC package to the PCB.
Many types of IC packages exist. One such type of IC package is a ball grid array (BGA) package. A BGA package has an array of solder ball pads located on a bottom external surface of a package substrate. Solder balls are attached to the solder ball pads. The solder balls are reflowed to attach the package to the PCB. In some BGA packages, a die is attached to the substrate of the package (e.g., using an adhesive), and signals of the die are interfaced with electrical features (e.g., bond fingers) of the substrate using wire bonds. In such a BGA package, wire bonds are connected between signal pads/terminals of the die and electrical features of the substrate. In another type of BGA package, which may be referred to as a “flip chip package,” a die is attached to the substrate of the package in a “flip chip” orientation. In such a BGA package, solder bumps may be formed on the signal pads/terminals of the die, and the die is inverted (“flipped”) and attached to the substrate by reflowing the solder bumps so that they attach to corresponding pads on the surface of the substrate.
Another example type of IC package is a quad flat package (QFP). A QFP is a four sided package that has leads extending from all four lateral sides. The leads are used to interface the QFP with a circuit board when the QFP is attached to the circuit board during a surface mount process. A type of IC package that is similar to the QFP is a quad flat no lead (QFN) package. Similarly to a QFP, a QFN package has four sides, but does not have leads that extend outward from the sides of the package. Instead, a bottom surface of the QFN package has contacts/lands that may be referred to as “pins.” The contact pins interface the QFN package with a circuit board when the QFN is attached to the circuit board during a surface mount process.
The dies in IC packages typically generate a great amount of heat during operation. Thus, IC packages are frequently configured to disperse the generated heat so that their operation is not adversely affected by the generated heat. For example, an external heat sink may be attached to an IC package to disperse heat. External heat sinks are effective solutions to improving the thermal performance of a package. However, in many cases, the package geometry creates additional complexities in the mounting of such heat sinks.
Furthermore, during operation, some ICs emit electromagnetic radiation and/or are sensitive to received electromagnetic radiation. As such, some IC packages need electromagnetic interference (EMI) shielding. In such cases, a metal EMI shield may be used in an electronics system to provide EMI shielding for the resident IC package. Such an EMI shield needs to substantially surround the IC package to provide effective EMI shielding. As such, a typical EMI shield forms a metal box that encloses the IC package.
Conventional electronics system designs that require both heat sink and EMI shielding have problems with cost and efficiency. In one example, an external heat sink is mounted underneath the EMI shield such that the EMI shield will enclose the external heat sink. From a thermal perspective this may be an acceptable solution, but from a cost and design perspective it is grossly inefficient because the EMI shield dimensions would have to be enlarged excessively to fit an adequately-sized heat sink underneath. Another existing solution is to directly embed a large heat spreader into an electronic product enclosure. In this solution, the EMI shield is attached to a larger heat spreader that has been integrated into the enclosure using some form of thermal interface material, creating a thermal path for the heat to dissipate. This has the advantage of maintaining a small EMI shield size, but requires a larger and costlier heat spreader that spans the entire area of the product chassis to dissipate heat. According to still another existing solution, the heat sink is mounted above the EMI shield. This solution does not add cost other than a nominal-sized EMI shield and heat sink, but proves to be an ineffective thermal solution because of the several thermally resistive interfaces that heat has to travel through before being received by the heat sink.